Induction heating coil



March 19, 1963 E. F. MOBRIEN 3,081,989

INDUCTION HEATING COIL Filed April 20, 1960 INVENTOR EDWARD F. McBRIENFIG. 4 50 ATTORNEY United States Patent 3,081,989 INDUCTION HEATING COILEdward F. McBrien, Parrna, Ohio, assignor to The Ohio CrankshaftCompany, Cleveland, Ohio, a corporation of Ohio Filed Apr. 20, 1960,Ser. No. 23,449 4 Claims. (Cl. 266-4) This invention relates toinduction coils of the type adapted for use in heating applications, andmore particularly to an induction heating coil characterized in having alarge number of turns confined within a limited amount of space. Suchinductors are useful, for example, in hardening and hot-machiningapplications where, due to space limitations, it is impossible to obtainthe desired number of coil turns using conventional coil construction.

As is'well known, increasing the number of turns'in an induction heatingcoil increases the coil efiiciency, decreases the required inductorcurrent, and makes it possible to more accurately control the heatpattern produced by the coil. Furthermore, in'some cases a largernumberof turns eliminates the need for a transformer and its associated heavybus bars leading to the coil.

In theusual induction heating coil, a copper tube or the like is woundin one or more turns to produce the desired heating pattern, with theheat generated in the coil being carried away by a cooling fluid whichflows through the hollow copper tube. Since the copper tube has asubstantial width, an inductor of this type having the desired number ofturns may require a larger amount of space than that available for theapplication at hand. In the hotmachini'n'g field, for example, it isfrequently desirable to progressively heat the metal immediatelyadjacent the cutting tool. Due to space limitations, only a few turnsare possible in 'a conventionalinductor due to the width of theaforesaid'coppe'r'tube. Thus, the required currents are relatively largeand necessitate a transformer which must be mounted adjacent the cuttingtool or heavy flexible leads must be employed to carry the inductorcurrents to the coil. "These requirements have restricted the use ofinduction heating in this and other fields where space limitations areimportant.

As an overall object, the present invention seeks to provide a new andimproved induction coil arrangement having a maximum number of turns fora given amount of space whereby the coil efiiciency may be increased andthe required inductor current decreased with more accurate control ofthe resulting heat pattern.

More specifically, an object of the invention is the provision of aninduction heating coil formed from a plurality of turns of continuouslength of flat metal strip wound in a spiral configuration whereby thelong transverse sides of successive turns of the spiral lie adjacenteach other, in combination with insulation between the turns of thespiral at the edges of the strip to provide a continous passagewaybetween the turns through which a cooling fluid may pass. Thus, whereasthe cooling fluid was conducted through the center of the coil itself inprior art assemblies, the present invention provides an arrangementwherein the cooling fluid is conducted between successive turns of theinductor.

Still another object of the invention is to provide an induction coilassembly particularly adapted for use in fillet hardening applications.

The above and other objects and features of the invention will becomeapparent from the following detailed description taken in connectionwith the accompanying drawings which form a part of this specificationand in which:

FIGURE 1 is atop or plan view of an induction coil constructed inaccordance with the teachings of the present invention and adapted foruse in the heating of fiat sur faces and the like;

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FIGURE 2 is a cross sectional view taken along line II-II of FIGURE 1;

FIGURE 3 is an enlarged illustration of another embodiment of theinvention particularly adapted for use in fillet hardening applicationsand incorporating integral quenching means; and

FIGURE 4 is an illustration-of still another embodiment of the inventionadapted for use in heating elongated workpieces.

Referring to FIGURES 1 and 2, the coil shown is of the pancake typewhich may, for example, be used to heat the surface of a metal strip 10or other similar 'flat surface. As shown, the inductor comprises acontinuous length of solid copper strip "12 wound in a spiral about anaxis extending parallel to the long transverse dimension of the strip.As an example, the coil maybe formed from copper strip having athickness of inch and a width of 1 inch; however, 'the particulardimensions of the strip will, of course, depend upon thecurrent-carrying capacity of the coil. In any event, the width .of thestrip should be at least three times its thickness 'to achieve theadvantages outlined herein. A U-shaped strip of insulation 14 is slippedover the longitudinal edges of the copper strip 12 before it is woundinto a spiral, although it could be ap plied afterthe coil is formed. Toform the coil, the strip with the insulating strips 12 applied 'to itsedges, is rolled up or coiled to provide a continuous passageway 16between the successive turns of the coil which are sealed at theiropposite edges. A suitable adhesive may be'applied to the strip 12before coiling or the finished coil may be potted in accordance withknown procedures. The ends of the passage 16 are sealed as at 18 and 20whereby a cooling fluid maybe passed through the passageway betweeninlet and outletport's 22 and 24, respectively. Electrical leads 26 and"28 are provided 'for connection to a suitable source of "alternatingcurrent voltage, not shown.

It will readily be seen that since the thicknessof the "copper strip 12is very small, a large number of turns may be produced in the coil foragiven amount of space. Thus, the coil may be employed in installationswhere a conventional coil of a similar number of turns would be toolarge.

Referring to FIGURE 3, the workpiece 30 may be a flanged axle shaft orthe like having a fillet as at 32. In order to harden this fillet it isnecessary to induce currents in the flange portion 34 as well as in themain shank 36 of the workpiece. This would be difiicult with aconventional inductor due to space requirements. By employing theinductor shown in FIGURE 3, however, the desired result may be effected.This inductor again comprises a continuous length of solid copper strip38 having a width many times its thickness; but in this case the widthof the strip continuously varies to provide turns of varying widths inthe inductor. Continuous U-shaped strips of insulation 40 are againslipped over the longitudinal edges of the strip before it is formedinto a coil. In this embodiment, however, a third strip of insulatingmaterial 42 is disposed between the successive turns of the coil betweenstrips 40 to thereby divide the coil into two separate passageways 44and 46. The strips 40 at the inner periphery of the coil assembly areprovided with apertures through which tubes 48 extend. Thus, when aquenching fluid is conducted through the passageway 46 via inlet andoutlet ports 45 and 47 it will pass through the tubes 48 and onto thesurface of the fillet or other portion of the workpiece being treated.At the same time, a cooling fluid may be forced through the passage 44via ports 49 and 51 to carry away the heat generated in the strip 38.Electrical leads, not shown, are again connected to the opposite ends ofstrip 38 as in the embodiment of FIG- URE 1. Actually, the currentdensity will be greater at the inner periphery of the strip 38 which isremoved from the cooling passage 44. However, the heat generated at 3the inner periphery of the strip will be readily conducted to the outerperipheral portion where it may be transferred to the cooling fluidconducted through passage 44.

In FIGURE 4, still another embodiment of the invention is shown whereina solid copper strip 50 is wound in a spiral configuration about an axisextending parallel to the short transverse dimension of the strip. Theconstruction of the coil in this case is similar to that of FIG- URE 1and includes U-shaped strips of insulating material 52 applied over itsedges. As will be understood, cooling fluid and electrical connections,not shown, are provided. It will be noted that the curvature in thestrip is now across its width rather than its edge. With thisarrangement, a large number of turns can be produced in the coil over arelatively short length. Thus, the coil is particularly adapted for usein heating elongated workpieces where space requirements are aconsideration.

Although the invention has been shown in connection with a specificembodiment, it will be readily apparent to those skilled in the art thatvarious changes in form and arrangement of parts may be made to suitrequirements without departing from the spirit and scope of theinvention.

I claim as my invention:

1. An induction coil comprising a continuous length of solidelectrically conductive strip material having a width many times itsthickness and wound in a spiral configuration in which the longtransverse sides of the strip material lie adjacent each other,insulation disposed between the turns of the spiral at the oppositeedges of the strip material to provide a continuous passagewaybetweenthe turns, means for sealing the opposite ends of the passageway,and connections communicating with said opposite ends for conducting acooling fluid through the passageway.

2. An induction coil comprising a continuous length of solidelectrically conductive strip material having a width many times itsthickness and wound in a spiral configuration having successive turns inwhich the long transverse sides of the strip material lie adjacent eachother, U-shaped strips of insulating material with the insulating stripson successive turns of the spiral abutting each other to provide acontinuous passageway between the turns, and

means for conducting a cooling fluid through the passageway.

3. An induction coil comprising a continuous length of solidelectrically conductive strip material having a width many times itsthickness and wound in a spiral configuration in which the longtransverse sides of the strip material in successive turns of the spiralface each other, continuous lengths of insulating material disposedbetween the turns of the spiral to provide two separate and continuouspassageways between the turns, spaced openings in one of said continuouslengths of insulating material adjacent a peripheral edge of the coil,means for injecting a quenching fluid into said one passageway wherebythe quenching fluid may pass through the openings in said one length ofinsulating material and onto the surface of a workpiece disposed withinthe coil, and connections for conducting a cooling fluid through theother of said passageways.

4. An induction coil comprising a continuous length of solidelectrically conductive strip material having a width many times itsthickness and wound in a spiral configuration in which the longtransverse sides of the strip material in successive turns of the spiralface each other, continuous lengths of insulating material disposedbetween the turns of the spiral at the opposite edges of the stripmaterial and at the center thereof to provide two continuous passagewaysbetween the turns, spaced openings in the continuous length ofinsulating material at the edge of the strip material which defines theinner periphery of the coil, means for injecting a quenching fluid intothe passageway communicating with said openings whereby the quenchingfluid may pass through the openings and on to the surface of a workpiecedisposed within the coil, and connections for conducting a cooling fluidthrough the other of said passageways.

I References Cited in the file of this patent UNITED STATES PATENTS2,481,071 Bowlus Sept. 6, 1949 2,863,130 Gray et al Dec. 2, 1958 FOREIGNPATENTS 293,200 Switzerland Dec. 1, 1953 730,104 Great Britain May 18,1955

4. AN INDUCTION COIL COMPRISING A CONTINUOUS LENGTH OF SOLIDELECTRICALLY CONDUCTIVE STRIP MATERIAL HAVING A WIDTH MANY TIMES ITSTHICKNESS AND WOUND IN A SPIRAL CONFIGURATION IN WHICH THE LONGTRANSVERSE SIDES OF THE STRIP MATERIAL IN SUCCESSIVE TURNS OF THE SPIRALFACE EACH OTHER, CONTINUOUS LENGTHS OF INSULATING MATERIAL DISPOSEDBETWEEN THE TURNS OF THE SPIRAL AT THE OPPOSITE EDGES OF THE STRIPMATERIAL AND AT THE CENTER THEREOF TO PROVIDE TWO CONTINUOUS PASSAGEWAYSBETWEEN THE TURNS, SPACED OPENINGS IN THE CONTINUOUS LENGTH OFINSULATING MATERIAL AT THE EDGE OF THE STRIP MATERIAL WHICH DEFINES THEINNER PERIPHERY OF THE COIL, MEANS FOR INJECTING A QUENCHING FLUID INTOTHE PASSAGEWAY COMMUNICATING WITH SAID OPENINGS WHEREBY THE QUENCHINGFLUID MAY PASS THROUGH THE OPENINGS AND ON TO THE SURFACE OF A WORKPIECEDISPOSED WITHIN THE COIL, AND CONNECTIONS FOR CONDUCTING A COOLING FLUIDTHROUGH THE OTHER OF SAID PASSAGEWAYS.